This invention relates to a process for the production of powdered metallic cobalt and, more particularly, relates to a process for the production of powdered metallic cobalt by reduction of cobaltous ammonium sulphate solutions.
A method for the production of cobalt from aqueous cobaltous ammonium sulphate solutions by reduction with gaseous hydrogen at elevated temperatures and pressures was disclosed in a paper entitled The Hydrometallurgical Production of Cobalt published in the Transactions, CIM, 65(1962), 21-25 by W. Kunda, J.P. Warner and V.N. Mackiw. In the nucleation stage, reduction is initiated and fine metal particles or nuclei are formed in the solution. In the densification stage, metal is precipitated from solution onto the preformed "seed" particles to produce larger particles. This latter step is repeated until the powder reaches the desired size.
In order to initiate the formation of the metal particles during the nucleation stage, a nucleation catalyst must be added to the aqueous metal salt-containing solution. The method developed by Kunda et al, and in commercial use by Sherritt Gordon Limited, was a mixture of sodium sulphide and sodium cyanide to promote nucleation of cobalt powder. This method can be used to produce powders of less than 25 microns in size; however, the powder is relatively high in sulphur and carbon content (0.3 to 0.8% C and 0.2 to 0.5% S). When powders of finer size are required, the carbon and sulphur levels normally are higher since fewer densifications result in less dilution of the initial carbon and sulphur in the nucleation powder.
In addition to the potentially high carbon and sulphur levels reporting to the product powder, the use of sodium cyanide is undesirable because of its toxic nature.
It is a principal object of the present invention to provide a process for the production of spherical or nodular cobalt powder having an average particle size less than 25 microns, as measured by FSSS, with low carbon and sulphur contents.
It is another object of the present invention to provide a process which does not require sodium cyanide for the nucleation of fine cobalt powder.